1. Field of the Invention
The present invention relates to an improvement of the head of a wood-type golf club, made substantially of wood, and known as a number one wood, i.e., a driver.
2. Description of the Related Art
In general, golf is played with a plurality of golf clubs comprising a set. A certain relationship must exist between the golf clubs in the set, to provide a balanced swing weight or a constant swing feeling, and thus the weight of the head of each golf club must be restricted. In the case of the driver, it is considered that the weight of the head should be approximately two hundred grams, and therefore, this weight restriction must be taken into account when designing a driver.
U.S. Pat. No. 1,538,415, issued to M. Tootle 3D, et al. on May 19, 1925, discloses a typical driver having a wood-type club head with a sole plate attached to the bottom surface thereof. The sole plate in this patent carries a weight. As is well known, the wooden head of the driver has a solid structure and a weight such as a block of lead is inserted in the wooden head to adjust the weight thereof as desired.
Other types of drivers made of metallic materials are known. For example, U.S. Pat. No. 4,313,607, issued to Thompson on Feb. 2, 1982, discloses a metallic head of a driver comprising a contoured hollow metallic shell, synthetic plastic material filled in the interior cavity of the shell, and a reinforcing strut extending transversely and between the walls of the shell, and U.S. Pat. No. 4,021,047, issued to Mader on May 3, 1977, discloses a metallic head of a driver comprising a contoured metallic shell with an upper opening and a wooden cap fitted on the upper opening to form an air chamber within the club head. In contrast to the wooden club head, the weight of the metallic head of a driver can be adjusted by providing a cavity or a chamber within the metallic shell.
Nowadays, a wood-type club head having a solid structure is popular with many players, because the feel of the wooden club head upon impact with a golf ball is superior to that engendered by the metallic club head having a hollow structure, or by a fiber reinforced club head. However, the weight of the conventional wooden club head for a driver must be restricted to approximately two hundred grams, and thus the size of the head is restricted. Specifically, a length of the head, as viewed transversely of the head, or measured horizontally between a front end and a rear end thereof from the viewpoint of the swing of the golf club, is necessarily less than 80 millimeters. As a result, the moment of inertia of the wooden club head, which is calculated around a vertical axis passing through the center of gravity of the head, becomes smaller than that of the metallic hollow head, bringing a disadvantage to the wooden club head in that the direction of flight of the golf ball will not be always as desired and the distance of flight will be reduced if the player hits the golf ball at a point other than the sweet spot of the club head. Therefore, it is difficult for a beginner to obtain a stable drive with the driver.